Lead Keel Modification

Discussion in 'Boat Design' started by Dick Flower, Apr 25, 2007.

  1. Dick Flower
    Joined: Apr 2007
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    Dick Flower Junior Member

    Hello everyone, I just found this Forum while looking for some help with my boat.

    I have a 1972 Challenger 32 (built in California) and want to modify the keel so that I can use her in the French canals. I would like to reduce draft by approximately 6 inches, to equal that of the skeg. The present draft is about five feet (1m50). The Canal du Midi is sadly silting up and now has a guaranteed depth of only 1m40. When I first travelled down it in 1980 it had a depth of 1m80.

    I have been thinking about this for some time without making a decision, but I have now sold our mooring, and have to move the boat. We haven't sailed her for 3 years, I can't sell her for an acceptable price, as I've spent too much on her, and we would at least use her more in the Canals.

    I originally considered cutting off part of the keel and putting the material removed in the bilge, or removing the keel completely, cutting it up and putting it in the bilge.

    My latest thought is that it should be possible to remove the keel, reduce the depth of the bilge by cutting material from the bottom, fix the keel back, and fair it into the hull, which would be a much neater job.

    As the boat is very stiff in both pitch and roll I think that the resultant raising of her CofG would be an improvement, especially when the mast is laid on deck for the canals.

    I removed the nuts on the keel studs and lowered the keel a couple of inches about 15 years ago to re-seal the joint to the hull. The flat bottom of the bilge did not seem to be reinforced, just very thick and uneven laminate, so I levelled this off by pouring resin in and added a stainless steel plate, bedded on the resin, to carry the load of the keel bolts.

    I guess if I cut off the bottom of the bilge I will find out if there is any original reinforcement there!

    Does anyone here know anything about the Challenger 32, GRP building techniques in the 1970’s, or have any comments or suggestions, please.

    [​IMG]
     
    Last edited: Apr 25, 2007
  2. Gramp34
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    Gramp34 Junior Member

    Yes, it is possible to shorten the keel stump as you suggest to reduce draft. You would need to determine the current laminate schedule in the sides and bottom by grinding back the existing material layer by layer. You'll most likely find alternating layers of woven roving and mat. Then you duplicate that laminate schedule in the new keel stump bottom with epoxy resin instead of polyester.

    "The Fiberglass Boat Repair Manual" by Allan H. Vaitses gives a good description of the details involved.

    You don't say you want to modify the boat because you love it and want to keep it, so I'm assuming this is a business decision you're making.

    In accounting there is a term called "sunk cost". It means the money thats been put into an asset but can't be recovered. Rational decisions don't include consideration of sunk cost.

    You're proposing a major re-engineering of this boat. It's going to cost considerable time and money if you do it yourself, and will cost far greater money if you contract it to a qualified yard. When you do decide to give up this boat, any surveyor will find this modification. Unless you can show receipts from a reputable yard for the work, the market is going to value the boat as a home-built of unknown quality. (What would you pay for a boat with major structural rework done by someone with no fiberglass experience?) You'll also have a boat that doesn't sail as well and still makes a marginal canal boat.

    So, because you can't get your investment out of this boat now, you're proposing to put even more money into it while reducing its market value below what it is now? This is why business decisions shouldn't consider sunk cost.

    If you want a canal boat, why don't you see if anyone has one they'll swap you for your sailboat? If you don't, maybe it's time to cut your losses.

    Good luck,

    Tim
     
  3. alan white
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    alan white Senior Member

    Looks like half of the keel will remain if 6" is chopped. I gather this is an external keel, since you said you had once lowered it.
    I guess if you removed the keel completely, the keelbolts could be shortened and rethreaded. The bottom 6" removed, if recast, could be added to each side of the remaining "stump" using stainless drifts. THEN it's time to do a layup and completely enclose the new keel with epoxy/glass to lock the new castings in place.

    A.
     
  4. Dick Flower
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    Dick Flower Junior Member

    Thanks, Gramp, for the helpful info', I think I'll have to look at the Vaitses book you mention.

    Well, I wouldn't say something soppy like that here, would I? But I have spent nearly 20 years working on the boat, even if I didn't have much time for sailing.

    I have plenty of time available, if not money, but time on the hard is not too expensive here, and it's not that big of a job. Before we specialised in AC&R my company (me at that time) undertook general maintenance work. I have only done a few structural jobs on GRP hulls personally, but having paid professionals to do these jobs I was often left with the feeling I could have done better myself. i.e. I won't be contracting the work to anyone.
    I no longer plan to sell the boat; my kids can have it eventually.

    I think that is debatable; I feel the boat is over ballasted and too stiff, and that she could well sail better after my proposed changes. We sailed from Mallorca to S France (Course basically N) in a NE 7-8, making 9 kts, with 2 reefs in the main, and the rail well clear of the water. That's great, but at anchor in a chop you almost get thrown out of the forward bunks by the violent pitching.
    Having crossed France twice on the canals, I think she'd make a great canal boat. I don't need a floating Winnebago, and I can step the mast and go sailing again when I run out of canal.


    Thanks. I haven't been able to find anyone who wants to swap a canal boat for a sailing boat. I would sell her at a bargain price to someone who I thought appreciated her, but so far all I have had is bunch of w anchors.


    Thanks again for your reply, Gramp. I think I'm just going to follow my instincts.
     
  5. Dick Flower
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    Dick Flower Junior Member

    Yes, the keel is external. As the whole keel is enclosed in GRP (I chopped it away just along the joint and made it good after remaking the gasket), I don't know if the "bolts" are studs cast into the keel or bolts running right through the depth of the keel. Which do you think is the most likely?

    I also considered recasting the lead removed and adding it to the sides of the remaining lead keel, but simply shortening the bilge/stump by 6" seems less work, and would only raise the boat's CofG an inch or so, as displacement is about 6/7 tons.

    Also, the keel is slightly bulbous at the bottom, which further complicates cutting it shorter, and would seem to make keeping it in one piece more sensible.

    [​IMG]

    [​IMG]
     
    Last edited: Apr 25, 2007
  6. alan white
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    alan white Senior Member

    I guess the studs would be cast in. I misread your initial post.
    Relocating your fuel tank would allow raising the bilge bottom 6". Your ballast could remain as is (don't even unbolt it).
    So you would be cutting once completely around about 6" above the lead after removing the fuel tank, freeing the ballast.
    Temporarily roll the keel off to the side, still attached to the bilge pan.
    Taper the outside of the bilge pan attached to the keel and the inside of the keel shell attached to the boat to match (how thick? An inch?). Jack ballast keel section back up buttered with epoxy, so that the ballast part now rises 6" higher, fitting like a scarf joint inside the cavity. Then it's just a matter of grinding, glassing, and fairing the outside. Then inside lay up a schedule to reinforce the bottom 12" or so (this should be pretty close to the keel root, so access would be reasonable). Wouldn't hurt to add some mechanical fasteners either, like a bunch of 1/4" FH machine screws into tapped holes, after the assembly is cured.

    Alan
     
  7. Dick Flower
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    Dick Flower Junior Member

    Thanks for the suggestions, Alan.

    I'm not sure about grinding/refitting the bilge pan. I don't know the thickness of the keel stub sides, but the bottom is over 1 1/4" where I mounted a thru hull transducer. They didn't skimp on material in those days. The keel is not quite the shape shown in the drawing, it flares out both laterally and longitudinally from top to bottom, so that it is possible the lower part would not fit into the upper at all. I don't have a good picture to show this, but the one below may give some idea. This flaring is not noticeable inside the bilge, so I think there is a very thick layer of GRP (or filler), to fair the lead to the hull, immediately above the lead, or a lot of laminate inside to attach it.

    Also, a chunk weighing nearly a ton and a half might be a bit awkward to move around, trial fit, and position accurately. I don’t want to have the boat going in circles because the keel is not straight.

    I am beginning to think it would be best to unbolt and remove the lead keel, line it up carefully with the cut-off stub and hull, reattach it from inside with GRP and possibly metal reinforcement, and fair the outside as necessary. By cutting open the section removed I will know what was done originally.

    Assuming the studs are cast into the keel, I wondered how the builders attached it originally. I think it would have been near impossible to accurately drill holes in a thick bottom section for 8 or so cast-in studs, which are probably not even parallel. Can anyone suggest how it was done, and how this is done nowadays?

    I suspect that the keel was either put in the bottom of the mound before laying up the hull, or, more likely, offered up to the completed moulding and glassed and faired in. In both cases the nuts would be tightened up after the laminate cured.

    The reason I lowered the keel just after I bought the boat was because she was making water around the keel studs/bolts. I only dropped it a small amount, but from what I could see there was no gasket or sealant in the joint, it looked as if laminate had just been laid straight on the lead. From the uneven mess at the bottom of the bilge (probably because it is not so accessible that working down there is pleasant) it looked to me that they just laid a very large amount of material on the bottom and sides, on the basis of “the more the better”.

    Dick
     

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  8. Gramp34
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    Gramp34 Junior Member

    Hi Dick,

    I think I understand better now where you are coming from.

    Keel bolts in lead keels are commonly stainless rod bent into a J or L shape and cast into the lead. Sometimes they weld them into a grid before casting. Since your bolts aren't lined up very well, they probably aren't.

    Lots of production boats offered a shoal keel option. If you're lucky enough you might find your boat had that option, and can find the shape of the shoal keel. If you make a wooden pattern for the new keel, a lead foundry can melt your old keel and recast it into the new shape. They could even fish the keel bolts out of the ladle and reuse them in the mold. The foundry would be able to explain what they need from you.

    I'm going to suggest consulting with a naval architect. Here's why:

    There's a sailboat ratio calculator at http://www.image-ination.com/sailcalc.html that has the Challenger 32 data in it. You can compare yours against different boats. The thing that strikes me is the relatively low sail area to displacement ratio (13.4) which is almost in motorsailer territory.

    It also lists your displacement at 12800 lbs. The drawing you posted shows the ballast is 3200 lbs, for a ballast to displacement ratio of 25%. This sounds pretty low to me. You can download a spreadsheet at http://www.johnsboatstuff.com/Articles/fuzzy.htm with specs on over 1200 boats. I pulled the values for boats 30 to 35 feet and calculated the ballast to displacement ratio. 90% of the boats had ratios between 30% and 54%. The lowest was 26%. Your boat at 25% is on the edge of sailboat design practice.

    You mentioned you thought the boat is very stiff and therefore overballasted now. Let me suggest that it may seem stiff because it has relatively low sail area, and there might be considerable form stability offered by the shape of the hull (e.g., catamarans have negligible heel yet have no ballast at all -- all their stability comes from the hull form).

    Form stability can make a boat very stiff at low angles of heel, but past a certain point it rapidly diminishes. E.g., a catamaran starts really stiff, but if one hull gets very airborne, it goes right over very quickly, and stays inverted. Ballast give you weight (or reserve) stability that provides the righting moment to bring the boat back up level.

    This is where a naval architect can help with some calculations and expert opinion on the best ways to proceed. If you do decide to recast the keel, the shape is going to be important for performance, especially pointing ability, and the NA can give good advice on an efficient shape. There may be implications for the boat's stability even raising the existing keel 6". Best to find out what those implications might be before major surgery begins.

    Cheers,

    Tim
     
  9. Dick Flower
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    Dick Flower Junior Member

    Hi Tim,

    I found and ordered the Vaitses book on Amazon at a reasonable price.

    You have given me plenty of food for thought - nothing is simple on boats, is it?

    Bending rod for keel bolts sounds about right, but maybe they cut less corners in the 1970's? - it was a pretty expensive boat then. There is a small weep of rust from a slightly damaged area low down on the lead keel's GRP sheathing, which suggested to me that there is some iron inside the lead, perhaps a plate near the bottom into which the rods were fixed. Unless I find someone who worked for Challenger Yachts I guess I'll never know without cutting it open.

    I have some original contemporary Challenger brochures, but there is no mention of a shoal draft option.

    I don't think I'm going to find any lead foundries in France, at least not around here, where they are not really into making much except wine. Perhaps the relatively low ballast ratio is partly offset by the weight of the thick hull, the steel fuel tank and rather large engine installed quite low down?

    I think I already knew the initial stiffness comes from form stability, and didn't want to admit it. The bottom is almost flat, which is obviously going to make her bob about like a cork when anchored in choppy water.

    I agree that it would be wise to seek expert advice before starting major surgery. Even if I myself only use her in the canals I wouldn't like to think I might put some future owner in peril if he put to sea. I don't really know where to start on this nor what it would cost - presumably the cost would reflect the degree of responsibilty implied.

    Then again, to follow my Uncle's adage that "the first bloke had to do it" when faced with a problem, (Born in 1900, he started work at 8, served his apprenticeship in a steam traction engine factory, then served in the RN as an ERA in destroyers in WW1. He could fix absolutely anything when I was a kid!) I am tempted to just shorten the keel and then make a sea trial to see if any more ballast is needed.

    I hardly dare mention my next project, which is to cut off the keel stepped mast at deck level and put it in a tabernacle for easier raising and lowering....
     
  10. Gramp34
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    Gramp34 Junior Member

    Hi Dick,

    I wouldn't give up on finding a lead foundry in France. Somone's got to be making keels for all those Beneteaus, Jenneaus, etc. I just tired Thomas Global (an industrial directory) at http://www.thomasglobal.com and searched under lead castings in France. It came up with 23 companies.

    A naval architect should be able to work on an hourly basis for you. I've heard a price of $85 per hour around here. If you have the hull lines plan already, it can be scanned into a computer, traced and stability calculated. If not, you can take a bunch of hull measurements to get the offsets that can be used for calculation. In the overall scheme of things the NA should be a minor cost. You'll want to interview some to find one who'd be proficient at this type of job. Heck, with e-mail and fax, they can be anywhere in the world.

    My old man was a pretty clever guy although he didn't have much formal education, either. He taught me that it's good to learn from your mistakes, but it's even better to learn from the mistakes of others. ;) Unfortunately, you might not be able to see the effects of too little reserve stability until a knockdown occurs.

    As for changing to a deck-stepped mast, that's relatively easy. Find a similar sized boat with a tabernacle design that works well, and copy it. Cut the bottom off your mast and you can use either it or aluminum or stainless pipe as a compression post from the original mast step on the keel to the cabin roof under the new tabernacle. Bob's your uncle and you're done.

    Cheers,

    Tim

    P.S. I've found from working on these old boat that they were all essentially hand-made rather than mass produced. What's inside your keel may not match what's inside the keel of any other boat. You could get it x-rayed, but unfortunately lead is an effective shield against x-rays...
     
    Last edited: Apr 26, 2007
  11. alan white
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    alan white Senior Member

    If you can, it may be possible to grind a bit off the bottom of the lead ballast and see if there are pockets within which nuts/rod ends are hidden. If so, the ballast would have been drilled and not had rods cast in. dunno how thick that area is, but probably it's not very.
    If you see nothing but lead, then it would be harder to reattach the cut-off end later, should you want to do that. The rods are no doubt cast in that case.
    The other issue is WHERE the backing is inside the keel. If below the cut-off point, cutting the keel will leave only the shanks holding the remaining keel.
    If nutted at the bottom (rods thru drilled holes) then the rods should be removed entirely and shortened, pockets made on the new undersurface, etc..
    The best scenario is that the backing or bends are above the 6" cut point.
    otherwise, I would imagine you'd have to chisel out some lead and thread in place the rod ends, which wouldn't be fun.
    Worst is if you know the rods are cast in, but you see sparks flying out when you're cutting.

    Alan
     
  12. Gramp34
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    Gramp34 Junior Member

    I'm going to add one check before you do this. A keel stepped mast provides more support for the bottom of the mast that a deck stepped mast, so can be made slightly smaller (about 5%) in dimension.

    To check your mast is strong enough for deck stepping, Dave Gerr's book "The Nature of Boats" has some rules of thumb on pages 291-2 for masts with a single set of spreaders. Take the height of the mast from the deck to top and divide by 85. The width of the mast cross section should be at least this wide. The length of the cross section should be at least 1.4 times the width. The wall thickness should be at least 1/35th the width of the section.

    If your mast section meets these values, the mast will be strong enough. If it doesn't, it may still be strong enough for deck stepping, but a naval architect will need to do some calculations to verify that.

    Cheers,

    Tim
     
  13. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    If you will travel mainly on canals and sheltered water, maybe it isn't a big deal with slightly higher cg, slightly smaller displacement and the mast on deck?
    Also, if stability is reduced that is good for the mast. Spar-makers often dimension the mast according to rightening moment at 30 degrees.
     
  14. Gilbert
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    Gilbert Senior Member

    I think your boat would be fine with 25% ballast ratio as long as you have sails that allow reefing. My suggestion would be to recast the keel as a winged keel. That should easily gain more than 6 inches. And the mast tabernacle should work fine also.
     

  15. alan white
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    alan white Senior Member

    ... Remembering that the boat will also be narrower at the waterline at a lower displacement, and so be initially more tender (unless the ballast is replaced somehow). On the other hand, removing 4" of ballast might very well yield 5" of increased clearance depending on ballast ratio if the weight isn't replaced, so the amount removed and whether or how much of it is replaced will be a decision between initial stability and final stability.

    Alan
     
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